Human chorionic gonadotropin (hCG) is a glycoprotein secreted by the placenta and excreted in the urine. Urinary levels of hCG are highest during the first trimester of pregnancy. Because of these facts, the detection of hCG in urine by way of diagnostic tests has been used in pregnancy determination kits and tests.
The glycoprotein itself has two sub-units, the sequence of which has been published. Morgan et al. "The Amino Acid Sequence of Human Chorionic Gonadotropin", The Journal of Biological Chemistry, 250(13):5247-5258 (1975).
Over the years, various investigators have worked on assays for hCG which would be both sensitive and specific and which would be useful as an early indication of pregnancy. In some cases, synthetic peptides of various lengths and amino acid sequences have been designed for potential use in binding to anti-hCG. For example, U.S. Pat. No. 4,400,316 to S. Katsuragi et al. relates to a peptide taken from the C-terminal fragment of hCG which comprises an amino acid sequence including fragment [127-145]. This patent refers to the synthesis of various protected hCG fragments in making the intended end-product including several containing six and seven amino acid residues: P(140-145); P(139-145); P(132-137); P(106-111); and P(105-111).
U.S. Pat. No. 4,804,626 to D. Bellet et al. describes an immunometric assay for the detection of hCG. It indicates that certain cell lines recognized antigenic determinants in certain residues of the C-terminus peptides: FB12 recognizing residues 110-116 and FB08 and FB09 recognizing residues 134-145, particularly the glycosylated 134-139. Bellet and co-workers synthesized certain subpeptides of lengths between five and ten amino acid residues: 110-116 and 139-145.
It would be an improvement in the art to have easily synthesizable short peptides having the antigenicity of a portion of the .beta.-chain of hCG for use especially in diagnostic test kits.